I can't use my full balance from Google Opinion Rewards.

I have $13.12 in my wallet, as shown in the Opinion Rewards app, and through the Play Store under payment methods. I was trying to buy some Minecoins and when I go to check out, only $5.64 is showing in my wallet. When I try making an in app purchase from another game, the full amount ($13.12) is available to use. Is this just a thing with Minecraft?